Hi Mark, Yes, in fact I did that. I used a BMS to build my “home” battery with 90 LFP cells for a total of 80Kwh. I didn’t meant for a UPS replacement for lead-acid you should add a BMS, because they already have an small internal BMS, as they have inside multiple LFP cells, and yes, they also have choices with bluetooth. In fact, this is the way I replaced my car lead-acid battery, which previously was dying every 2-3 years. It is true that if your UPS has multiple lead-acid cells, because they most of the time are in series, they will not be automatically balanced. What I do in those cases is fully charge each cell before using them. If they are new and grade “A”, normally, unless there is faulty cell, they will remain balanced across multiple years. In fact, I tested that with an APC UPS with hast 4 20Ah lead-acid cells, and 4 external ones. Replaced with LFP ones, and after a couple of years, they were still balanced. Checked again after 2 more years, and still are balanced. Of course, if they have also bluetooth, you will be able to check that without removing them, as it allows to see the SoC of each individual cell (voltage is not good enough with LFP). Regarding price it may depend on each market, of course. Here a 8Ah 12V small cell (the one mostly used for UPSs up to 1600VA or so) cost 11-12 Euros, while the LFP one is around 38 (without bluetooth). Those prices aren’t including VAT (21% extra). Regards, Jordi @jordipalet
El 7 abr 2025, a las 11:38, Mark Tinka <mark@tinka.africa> escribió:
On 4/7/25 09:02, jordi.palet--- via NANOG wrote:
Agree, LFP is the way to go. I did that in many types of UPS, different models & capacity, such as EATON and APC, but many others as well.
There are many suppliers, even in Amazon, Alibaba, Aliexpress, etc. that already have LFP cells that internally have the BMS and work in a transparent way to replace lead-acid, using same connectors and dimensions (but much lower weight). They are more expensive (3-4 times the price of the lead-acid ones), but they will last for 15-20 year, and they can be discharged up to 90% instead of 50%. They often provide a bit “extra" real power/capacity as well.
If you are going to build your own Li-Ion battery, a BMS is a must.
But if you buy a pre-built Li-Ion battery, it will always ship with a BMS.
In fact, many of the 12V Li-Ion batteries may be purchased with a Bluetooth controller option, which gives you real-time data of the BMS's performance via a phone app.
I wouldn't say Li-Ion batteries are 3 - 4 times the cost of LA. At least in our market, you're looking at 2X, for just a pre-built battery with a BMS. If you want a larger system (24V or 48V), then yes, the extra controls, protections, build structure, e.t.c. can contribute to a 4X price difference.
The only issue with using 12V Li-Ion batteries in a UPS is that most UPS's are 24VDC systems. That means you'll need 2x 12V Li-Ion batteries... the problem being that you'd have to balance them, and external balancers don't fit well inside small UPS chassis.
Mark.
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